Taxonomy & naming
Albert Günther described Helogenes marmoratus in 1863 from the Essequibo River, Guyana. The Catalog of Fishes (Eschmeyer, CAS) gives Helogenes marmoratus Günther, 1863 as valid. It is placed in Cetopsidae, a family best known for the whale catfishes, though Helogenes is a small, quiet relative.
Morphology
FishBase gives a maximum of 3 in SL. The body is slim and marbled, with a long anal fin, and the fish swims on its side in undulating movements. When it rests on its side and stays still it can pass for a piece of dead wood.
Habitat
FishBase describes a typical inhabitant of black or clear waters, usually in forest streams with moderate to swift current over firm sand or gravel. It lives hidden under plants, litter or plant debris. The range covers the Atlantic drainages of Guyana, Suriname and French Guiana, the upper Río Orinoco and Río Negro systems in Venezuela, and the Amazon basin in Brazil, Peru and Ecuador. FishBase gives 72–79 °F and pH 6.0 to 7.0, with hardness up to 15 dH.
Feeding
FishBase reports that the fish feeds mainly on terrestrial insects, particularly ants, which fall into forest streams. It is nocturnal. In an aquarium it takes small live and frozen foods such as bloodworm, daphnia and small insects.
Mating
Courtship and spawning behaviour are not recorded in the available sources.
Breeding
No breeding record is available for this species.
In the aquarium
A quiet, secretive catfish for a mature tank with soft cover. Provide leaf litter, roots and shade, with a sand or fine gravel floor and some current. It feeds at night, so offer food after lights out and watch that it is eating. Keep it with peaceful small fish that stay out of its way. FishBase gives 72–79 °F, pH 6.0 to 7.0 and hardness up to 15 dH.
Conservation
The IUCN Red List assesses Helogenes marmoratus as Least Concern (assessment of 20 October 2020). The species is spread across a very large area of the northern South American forest streams.